diff options
Diffstat (limited to 'ast/erfa/dat.c')
| -rw-r--r-- | ast/erfa/dat.c | 306 |
1 files changed, 306 insertions, 0 deletions
diff --git a/ast/erfa/dat.c b/ast/erfa/dat.c new file mode 100644 index 0000000..c3b1836 --- /dev/null +++ b/ast/erfa/dat.c @@ -0,0 +1,306 @@ +#include "erfa.h" + +int eraDat(int iy, int im, int id, double fd, double *deltat ) +/* +** - - - - - - - +** e r a D a t +** - - - - - - - +** +** For a given UTC date, calculate delta(AT) = TAI-UTC. +** +** :------------------------------------------: +** : : +** : IMPORTANT : +** : : +** : A new version of this function must be : +** : produced whenever a new leap second is : +** : announced. There are four items to : +** : change on each such occasion: : +** : : +** : 1) A new line must be added to the set : +** : of statements that initialize the : +** : array "changes". : +** : : +** : 2) The constant IYV must be set to the : +** : current year. : +** : : +** : 3) The "Latest leap second" comment : +** : below must be set to the new leap : +** : second date. : +** : : +** : 4) The "This revision" comment, later, : +** : must be set to the current date. : +** : : +** : Change (2) must also be carried out : +** : whenever the function is re-issued, : +** : even if no leap seconds have been : +** : added. : +** : : +** : Latest leap second: 2016 December 31 : +** : : +** :__________________________________________: +** +** Given: +** iy int UTC: year (Notes 1 and 2) +** im int month (Note 2) +** id int day (Notes 2 and 3) +** fd double fraction of day (Note 4) +** +** Returned: +** deltat double TAI minus UTC, seconds +** +** Returned (function value): +** int status (Note 5): +** 1 = dubious year (Note 1) +** 0 = OK +** -1 = bad year +** -2 = bad month +** -3 = bad day (Note 3) +** -4 = bad fraction (Note 4) +** -5 = internal error (Note 5) +** +** Notes: +** +** 1) UTC began at 1960 January 1.0 (JD 2436934.5) and it is improper +** to call the function with an earlier date. If this is attempted, +** zero is returned together with a warning status. +** +** Because leap seconds cannot, in principle, be predicted in +** advance, a reliable check for dates beyond the valid range is +** impossible. To guard against gross errors, a year five or more +** after the release year of the present function (see the constant +** IYV) is considered dubious. In this case a warning status is +** returned but the result is computed in the normal way. +** +** For both too-early and too-late years, the warning status is +1. +** This is distinct from the error status -1, which signifies a year +** so early that JD could not be computed. +** +** 2) If the specified date is for a day which ends with a leap second, +** the UTC-TAI value returned is for the period leading up to the +** leap second. If the date is for a day which begins as a leap +** second ends, the UTC-TAI returned is for the period following the +** leap second. +** +** 3) The day number must be in the normal calendar range, for example +** 1 through 30 for April. The "almanac" convention of allowing +** such dates as January 0 and December 32 is not supported in this +** function, in order to avoid confusion near leap seconds. +** +** 4) The fraction of day is used only for dates before the +** introduction of leap seconds, the first of which occurred at the +** end of 1971. It is tested for validity (0 to 1 is the valid +** range) even if not used; if invalid, zero is used and status -4 +** is returned. For many applications, setting fd to zero is +** acceptable; the resulting error is always less than 3 ms (and +** occurs only pre-1972). +** +** 5) The status value returned in the case where there are multiple +** errors refers to the first error detected. For example, if the +** month and day are 13 and 32 respectively, status -2 (bad month) +** will be returned. The "internal error" status refers to a +** case that is impossible but causes some compilers to issue a +** warning. +** +** 6) In cases where a valid result is not available, zero is returned. +** +** References: +** +** 1) For dates from 1961 January 1 onwards, the expressions from the +** file ftp://maia.usno.navy.mil/ser7/tai-utc.dat are used. +** +** 2) The 5ms timestep at 1961 January 1 is taken from 2.58.1 (p87) of +** the 1992 Explanatory Supplement. +** +** Called: +** eraCal2jd Gregorian calendar to JD +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ +/* Release year for this version of eraDat */ + enum { IYV = 2016}; + +/* Reference dates (MJD) and drift rates (s/day), pre leap seconds */ + static const double drift[][2] = { + { 37300.0, 0.0012960 }, + { 37300.0, 0.0012960 }, + { 37300.0, 0.0012960 }, + { 37665.0, 0.0011232 }, + { 37665.0, 0.0011232 }, + { 38761.0, 0.0012960 }, + { 38761.0, 0.0012960 }, + { 38761.0, 0.0012960 }, + { 38761.0, 0.0012960 }, + { 38761.0, 0.0012960 }, + { 38761.0, 0.0012960 }, + { 38761.0, 0.0012960 }, + { 39126.0, 0.0025920 }, + { 39126.0, 0.0025920 } + }; + +/* Number of Delta(AT) expressions before leap seconds were introduced */ + enum { NERA1 = (int) (sizeof drift / sizeof (double) / 2) }; + +/* Dates and Delta(AT)s */ + static const struct { + int iyear, month; + double delat; + } changes[] = { + { 1960, 1, 1.4178180 }, + { 1961, 1, 1.4228180 }, + { 1961, 8, 1.3728180 }, + { 1962, 1, 1.8458580 }, + { 1963, 11, 1.9458580 }, + { 1964, 1, 3.2401300 }, + { 1964, 4, 3.3401300 }, + { 1964, 9, 3.4401300 }, + { 1965, 1, 3.5401300 }, + { 1965, 3, 3.6401300 }, + { 1965, 7, 3.7401300 }, + { 1965, 9, 3.8401300 }, + { 1966, 1, 4.3131700 }, + { 1968, 2, 4.2131700 }, + { 1972, 1, 10.0 }, + { 1972, 7, 11.0 }, + { 1973, 1, 12.0 }, + { 1974, 1, 13.0 }, + { 1975, 1, 14.0 }, + { 1976, 1, 15.0 }, + { 1977, 1, 16.0 }, + { 1978, 1, 17.0 }, + { 1979, 1, 18.0 }, + { 1980, 1, 19.0 }, + { 1981, 7, 20.0 }, + { 1982, 7, 21.0 }, + { 1983, 7, 22.0 }, + { 1985, 7, 23.0 }, + { 1988, 1, 24.0 }, + { 1990, 1, 25.0 }, + { 1991, 1, 26.0 }, + { 1992, 7, 27.0 }, + { 1993, 7, 28.0 }, + { 1994, 7, 29.0 }, + { 1996, 1, 30.0 }, + { 1997, 7, 31.0 }, + { 1999, 1, 32.0 }, + { 2006, 1, 33.0 }, + { 2009, 1, 34.0 }, + { 2012, 7, 35.0 }, + { 2015, 7, 36.0 }, + { 2017, 1, 37.0 } + }; + +/* Number of Delta(AT) changes */ + enum { NDAT = (int) (sizeof changes / sizeof changes[0]) }; + +/* Miscellaneous local variables */ + int j, i, m; + double da, djm0, djm; + + +/* Initialize the result to zero. */ + *deltat = da = 0.0; + +/* If invalid fraction of a day, set error status and give up. */ + if (fd < 0.0 || fd > 1.0) return -4; + +/* Convert the date into an MJD. */ + j = eraCal2jd(iy, im, id, &djm0, &djm); + +/* If invalid year, month, or day, give up. */ + if (j < 0) return j; + +/* If pre-UTC year, set warning status and give up. */ + if (iy < changes[0].iyear) return 1; + +/* If suspiciously late year, set warning status but proceed. */ + if (iy > IYV + 5) j = 1; + +/* Combine year and month to form a date-ordered integer... */ + m = 12*iy + im; + +/* ...and use it to find the preceding table entry. */ + for (i = NDAT-1; i >=0; i--) { + if (m >= (12 * changes[i].iyear + changes[i].month)) break; + } + +/* Prevent underflow warnings. */ + if (i < 0) return -5; + +/* Get the Delta(AT). */ + da = changes[i].delat; + +/* If pre-1972, adjust for drift. */ + if (i < NERA1) da += (djm + fd - drift[i][0]) * drift[i][1]; + +/* Return the Delta(AT) value. */ + *deltat = da; + +/* Return the status. */ + return j; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |